Expand index on ci_pipelines

For background see
https://gitlab.com/gitlab-org/gitlab/-/issues/292454#note_463034491

changelogs/unreleased/ab-ci-ref-index.yml

+---
+title: Expand index on ci_pipelines
+merge_request: 49604
+author:
+type: performance

db/migrate/20201209154746_expand_ci_pipelines_index_on_ci_ref_id.rb

+# frozen_string_literal: true
+
+class ExpandCiPipelinesIndexOnCiRefId < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  NEW_NAME = 'index_ci_pipelines_on_ci_ref_id_and_more'
+  OLD_NAME = 'index_ci_pipelines_on_ci_ref_id'
+
+  def up
+    add_concurrent_index :ci_pipelines, %i[ci_ref_id id source status], order: { id: :desc }, where: 'ci_ref_id IS NOT NULL', name: NEW_NAME
+
+    remove_concurrent_index_by_name :ci_pipelines, OLD_NAME
+  end
+
+  def down
+    add_concurrent_index :ci_pipelines, :ci_ref_id, where: 'ci_ref_id IS NOT NULL', name: OLD_NAME
+
+    remove_concurrent_index_by_name :ci_pipelines, NEW_NAME
+  end
+end

db/schema_migrations/20201209154746

+98e132fd1daadca14b4313783691c523290efdc81372ec8416bcea1a597376bf
\ No newline at end of file

db/structure.sql

@@ -20866,7 +20866,7 @@ CREATE INDEX index_ci_pipelines_for_ondemand_dast_scans ON ci_pipelines USING bt
 
 CREATE INDEX index_ci_pipelines_on_auto_canceled_by_id ON ci_pipelines USING btree (auto_canceled_by_id);
 
-CREATE INDEX index_ci_pipelines_on_ci_ref_id ON ci_pipelines USING btree (ci_ref_id) WHERE (ci_ref_id IS NOT NULL);
+CREATE INDEX index_ci_pipelines_on_ci_ref_id_and_more ON ci_pipelines USING btree (ci_ref_id, id DESC, source, status) WHERE (ci_ref_id IS NOT NULL);
 
 CREATE INDEX index_ci_pipelines_on_external_pull_request_id ON ci_pipelines USING btree (external_pull_request_id) WHERE (external_pull_request_id IS NOT NULL);